Re: [Jack-Devel] ALSA PCM multi plugin and xruns

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DateSun, 09 Dec 2012 11:43:54 +0100
From Stéphane Letz <[hidden] at grame dot fr>
ToJohn Rigg <[hidden] at jrigg dot co dot uk>
CcJack devel <[hidden] at lists dot jackaudio dot org>
In-Reply-ToJohn Rigg Re: [Jack-Devel] ALSA PCM multi plugin and xruns
Le 9 déc. 2012 à 11:45, John Rigg a écrit :

> On Sat, Dec 08, 2012 at 03:38:44AM -0800, Devin Anderson wrote:
>> IIUC, the 'xruns' are generated because there *is* data available to
>> be read, but there *isn't* enough data, which means 0 is returned,
>> which incorrectly indicates that an xrun happened.  The exception is
>> when both `capture_avail` and `playback_avail` are both set to 0.
>> Perhaps userspace hasn't been told about new samples in the kernel
>> ringbuffer.
>> 
>> I don't know whether this is a bug in the ALSA multi plugin or in
>> JACK.  I assume the problem is the multi plugin, as
>> `snd_pcm_hw_params_set_period_size` is called to constrain the period
>> size to one value, but I don't have enough of an understand of ALSA to
>> know for sure.  I'm hoping that someone on this list with a better
>> understanding of ALSA magic will be able to answer that question for
>> me.
> 
> This has been annoying me ever since I started using multiple
> ice1712 cards nearly 7 years ago. I never had the time to look
> into the cause. Thanks for investigating this.
> 
> John

This seems also to be the "long standing issue" that also occurs in jack2, since jack2 use the same ALSA code. Hopefully a fix for jack1/jack2 will be found.

Stéphane 
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